This paper introduces and experimentally validates a single-pixel imaging (SPI) system illuminated by a 90-140 GHz photonic noise source. The noise source, with a 36 dB excess noise ratio (ENR), proves to be an effective spatially-incoherent illuminator for SPI. High-fidelity reconstructions are achieved at sub-Nyquist sampling rates: the letters "T" and "H" attain structural similarity index (SSIM) values above 0.7 at 40-50% sampling, while the more complex letter "Z" requires a 70% sampling rate to reach an SSIM of 0.6. A key finding is that noise illumination significantly outperforms conventional 100 GHz single-frequency coherent illumination, achieving over 30% improvement in SSIM at equivalent sampling rates. This enhancement is attributed to the effective suppression of coherent interference speckles by the noise source's inherent randomness. Furthermore, we demonstrate the practical potential of this technique for security screening by successfully imaging a concealed metal blade.

Significant path loss at terahertz frequencies and the variation of antenna gain with distance pose key challenges for over-the-air (OTA) noise figure (NF) measurement of terahertz active integrated antennas (AIAs). This paper proposes a differential Y-factor OTA NF measurement method using a tunable photonic terahertz noise source with high excess noise ratio (ENR). The method eliminates the need for ENR calibration and ensures sufficient excitation power for OTA measurements under high-loss conditions. To further enhance accuracy, a dynamic gain calibration technique is introduced to address distance-related gain variation, enabling consistent NF measurements in both near-field and far-field scenarios. The effectiveness of the proposed approach is validated through measurements on a D-band (110–170 GHz) AIA. The NF measurement results show strong agreement with conducted reference values and consistent performance across different measurement distances.

Significant path loss at terahertz frequencies and the variation of antenna gain with distance pose key challenges for over-the-air (OTA) noise figure (NF) measurement of terahertz active integrated antennas (AIAs). This article proposes a differential Y-factor OTA NF measurement method using a tunable photonic terahertz noise source with a high excess noise ratio (ENR). The method eliminates the need for ENR calibration and ensures sufficient excitation power for OTA measurements under high-loss conditions. To further enhance accuracy, a dynamic gain calibration technique is introduced to address distance-related gain variation, enabling consistent NF measurements in both near- and far-field scenarios. The effectiveness of the proposed approach is validated through measurements on a D-band (110-170 GHz) AIA. The NF measurement results show strong agreement with the conducted reference values and consistent performance across different measurement distances.

Photoconductive terahertz emitters have proven to be crucial devices for generating terahertz radiation, which has broad applications in imaging, broadband spectroscopy, nonlinear spectroscopy etc. Traditional photoconductive terahertz emitters are typically stimulated by 800 nm lasers, however, face challenges such as integration and cost. A noteworthy alternative is the use of photoconductive terahertz emitters driven by 1550 nm lasers. This approach establishes a connection between terahertz technology and communication technology, offering the benefits of lower cost and compact integration. Consequently, it has emerged as an important area for future advancements of terahertz devices and systems. The properties of photoconductive materials are key factors in determining device performance. While important progresses have been made in development of 1550 nm photoconductive materials, many challenges still remain. This paper reviews materials of 1550 nm-pumped terahertz photoconductive emitters, including epitaxial layer structures, growth conditions, material treatment methods, and the influence mechanisms of various epitaxy or treatment conditions on material properties. Finally, factors influencing terahertz source devices and corresponding material optimization methods are summarized. This review aims to provide a foundation for improving the performance of terahertz photoconductive materials and devices, offering objective and practical guidance for researchers in this field.

We propose and experimentally demonstrate a universal millimeter-wave noise source based on an optically injected multi-mode chaotic laser. The wideband multi-mode chaotic lights are sliced, amplified and then converted into continuous-wave noise through a photodetector. In our approach, the center frequency and the excess noise ratio of the generated noise signal can be easily adjusted by controlling the sliced spectral numbers and intensities, respectively. Moreover, pulsed noise can also be obtained by introducing an amplitude modulation as a chopper. In our proof-of-concept experiments, we successfully generate 140-220 GHz and 220-390 GHz broadband noise signals with a tunable excess noise ratio up to 52.42 dB. We also validate the tunability of the operation frequency though generating three narrow-band noise signals with center frequencies at 140 GHz, 252 GHz, and 364 GHz, respectively. Furthermore, the generation of pulse noise with durations of 500 ns and 0.5 ns per period are experimentally demonstrated. These results confirm that our proposed universal noise source is a promising candidate for multiple application scenarios.

We present a rectangular waveguide-output photoconductive mixer addressing limitations in conventional free-space THz systems. The design integrates an extended hemispherical silicon lens photoconductive mixer with a linear pyramidal horn, enabling free-space to waveguide mode conversion in WR-2.2(330-500 GHz). CST simulations demonstrate operation from 330 to 500 GHz with an insertion loss better than −10 dB (maximum of −3.58 dB at 369 GHz). Theoretical calculations indicate an average output power of 26 nW across the WR-2.2 frequency range, peaking at 49.2 nW at 340 GHz. The structure achieves enhanced impedance matching and power transfer efficiency, providing a compact solution for integrated THz systems.

Terahertz noise sources have important application prospects in noise figure measurements. In this paper, a 0.4 THz broadband terahertz noise source based on a photoconductive antenna is proposed. As a demonstration of feasibility, this terahertz noise source is generated by mixing three beams of Gaussian-shaped incoherent light. The resulting excess noise ratio (ENR) across different frequency bands is as follows: 20.9 dB, with a flatness of ±7.9 dB in the 75~110 GHz range; 19.3 dB, with a flatness of ±6.2 dB in the 110~170 GHz range; 20.6 dB, with a flatness of ±4.8 dB in the 170~260 GHz range; and 18.7 dB, with a flatness of ±4.3 dB in the 260~400 GHz range. These results demonstrate that the terahertz noise source based on photoconductive antennas that we proposed shows great potential in high-frequency bands and noise figure measurements.

The In this letter, we propose a high-speed photoconductive detector with micro-sized plasmonic grating electrodes that support coupled plasmonic modes. The photoconductive InGaAs:Be layer was grown on InP substrate at 250 degrees C, on which the electrode parameters were optimized and fabricated. Both theoretical and experimental results demonstrate that the plasmonic effect was successfully excited by the micro-grating, and the responsivity was increased by 12 times as compared with the detectors without grating. An optical heterodyne system measurement showed a 3-dB bandwidth of at least 50 GHz. Furthermore, the structural error tolerances of the proposed device were studied, revealing significant improvement in fabrication stability.

We propose and experimentally demonstrate a wireless-channel key distribution scheme based on laser synchronization induced by a common wireless random signal. Two semiconductor lasers are synchronized under injection of the drive signal after electrical-optical conversion and emit irregular outputs that are used to generate shared keys. Our proof-of-concept experiment using a complex drive signal achieved a secure key generation rate of up to 150 Mbit/s with a bit error rate below 3.8 × 10−3. Numerical simulation results show that the proposed scheme has the potential to achieve a distribution distance of several hundred meters. It is believed that common-signal-induced laser synchronization paves the way for high-speed wireless physical-layer key distribution.

In this article, we present a terahertz photonic noise source by photomixing three Gaussian-shaped noise slices from a superluminescent diode. Experimental results demonstrate that terahertz noise with a frequency range of 200-390 GHz can be obtained with an excess noise ratio (ENR) up to 48 +/- 4.3 dB, corresponding to an equivalent noise temperature exceeding 10(7) K. Furthermore, the proposed noise source is used to measure the noise figure of a mature mixer product, holding the promise of generating terahertz noise at a higher frequency and with a larger bandwidth. The proposed photonic noise source possesses a high integration and raises the frequency range and the ENR of the noise spectrum to a new level.

Noise Figure(NF)is an important parameter in evaluating the performance of transmitting a sig-nal from a high-frequency electronic device.As the operating frequency increases,the NF of high-frequency electronic devices usually increases,and the Excess Noise Ratio(ENR)of existing noise sources cannot meet the associated measurement requirements.Therefore,to meet the measurement requirements for the NF of high-frequency electronic devices,we propose combining three incoherent optical beams into an unitraveling carrier photodiode(UTC-PD)based on incoherent optical mixing technology.A tunable terahertz(THz)photonics noise source with a high ENR in the 220-325 GHz frequency range is developed.The ENR can be tuned up to 45 dB.By using the Y-factor method,the proposed THz photonics noise source is applied to measure a THz mixer with large NF and negative conversion gain.The measured NF of the THz mixer ranges from 16 to 32 dB,the conversion gain is about-13 dB,and the uncertainty is 0.43 dB.The tunable THz photonics noise source with high ENR can meet the measurement requirements of THz electronic devices with high NF.It will play an important role in the measurement of NF of THz electronic devices and in guiding further optimization.

We propose and experimentally demonstrate a physical-layer key distribution scheme using commonly-driven laser synchronization with random modulation of drive light. Two parameter-matched semiconductor lasers injected by a common complex drive light are used as entropy sources for legitimate users. Legitimate users generate their own random signal by randomly time-division multiplexing of two random sequences with a certain duration according to individual control codes, and then independently modulate the drive light. Laser synchronization is achieved during time slots when the modulation sequences of two users are identical, and thus provide highly correlated randomness for extracting random numbers as shared keys. Experimental results show that the random modulation of the drive light reduces the correlation between the drive light and laser outputs. In addition, laser synchronization is sensitive to the modulation delay and then the latter can be used as an additional hardware parameter. These mean that security is enhanced. In addition, the proposed method has a short laser synchronization recovery time of lower than 1.1 ns, meaning a high rate of key distribution. The upper limit of final key rate of 2.55 Gb/s with a criterion of bit error rate of 1.68 × 10 −3 is achieved in experiments. Our results provide a promising candidate for protecting the security of optical fiber communication.

A millimeter-wave noise generation scheme is proposed in this paper. The scheme is based on a monolithically integrated dual-mode chaotic laser, which consists of a distributed Bragg feedback (DFB) section, a phase section, and an optical amplification section. The output spectrum state of the dual-mode laser can be controlled by adjusting the injection current in the three regions. The monolithically integrated dual-mode chaotic laser has stable chaotic output and can be used as a light source for integrated millimeter-wave noise source. As a feasibility demonstration, a dual-mode chaotic laser with a mode interval of 2.05 nm was generated in the experiment, the optical mixing on a photodetector produced millimeter-wave noise with a center frequency of 259 GHz and a bandwidth of 44 GHz (237-281 GHz), achieving a typical value of excess noise ratio of 47 dB. It has the advantages of high noise source utilization, small noise source volume, and high integration.

We propose and numerically demonstrate chaos synchronization of two vertical-cavity surface-emitting lasers (VCSELs) induced by common injection of constant-amplitude random-polarization light for physical key distribution. Results show that synchronization is sensitive to polarization rotation of injection light, and synchronization coefficients larger than 0.9 can be achieved as the rotation-degree mismatch is smaller than ±10°. Therefore, polarization rotation degree can serve as a hardware key parameter. Furthermore, each laser's output has no correlation to the constant amplitude of the injected light. Their components with identical polarization state, e.g. x or y polarization of VCSEL, also have low correlation coefficient smaller than 0.2. It is therefore believed that this synchronization scheme can provide a security-enhanced method of physical key distribution.

To guarantee information security from the lowest level of optical networks, it is essential to provide physical layer security in fiber-optic communication systems. However, it is challenging to realize high speed physical secure optical communication based on advanced optical modulation formats and pure commercial hardware components. In this work, we report an experimental demonstration of a high-speed 56 Gb/s PAM4 physical-layer secure optical communication system by employing an electro-optic self-feedback hardware module for temporal self-phase encryption and decryption without consuming any additional encryption channel. An encrypted 56 Gb/s PAM4 confidential signal is successfully decrypted after transmitting over 60 km single-mode fiber. The demonstrated scheme can not only be integrated with existing optical communication networks, but can also be used as a pluggable module, which may provide a promising solution for ultra-high speed physical secure optical communication by combining with advanced multiplexing technology in future.

Simultaneous generation and synchronization of multiple broadband laser chaos with different wavelengths are numerically demonstrated by using long-active-cavity Fabry-Perot (LC-FP) semiconductor lasers based on multi-mode beating effect. Simulation results show that the LC-FP laser under simple optical feedback can produce broadband chaos with a bandwidth up to 37 GHz with an active cavity length of about 1500 um. Furthermore, common-signal-induced chaos synchronization is predicted. Driven by a common chaos from the optical-feedback LC-FP laser, two response LC-FP lasers can reach broadband chaos synchronization with a correlation coefficient beyond 0.98. Meanwhile, the drive-response correlation is low at around 0.4. More interestingly, by optical filtering, parallel multiple broadband chaotic signals at different wavelengths are obtained with bandwidths exceeding 25 GHz and cross-correlation values lower than 0.2. The chaos synchronization keeps for the identical wavelengths. This work will pave a way for increasing capacity of chaos communication.

Optical chaos communication and key distribution have been extensively demonstrated with high-speed advantage but only within the metropolitan-area network range of which the transmission distance is restricted to around 300 km. For secure-transmission requirement of the backbone fiber link, the critical threshold is to realize long-reach chaos synchronization. Here, we propose and demonstrate a scheme of long-reach chaos synchronization using fiber relay transmission with hybrid amplification of an erbium-doped fiber amplifier (EDFA) and a distributed fiber Raman amplifier (DFRA). Experiments and simulations show that the hybrid amplification extends the chaos-fidelity transmission distance thanks to that the low-noise DFRA suppresses the amplified spontaneous emission noise and self-phase modulation. Optimizations of the hybrid-relay conditions are studied, including launching power, gain ratio of DFRA to EDFA, single-span fiber length, and number of fiber span. A 1040-km chaos synchronization with a synchronization coefficient beyond 0.90 is experimentally achieved, which underlies the backbone network-oriented optical chaos communication and key distribution.

Common-signal-induced laser synchronization promoted a promising paradigm of high-speed physical key distribution. Constant-amplitude and random-phase (CARP) light was proposed as the common drive signal to enhance security by reducing the correlation between the drive and the laser response in intensity. However, the correlation in light phase is not examined. Here, we numerically reveal that the correlation coefficient of the CARP light phase and the response laser intensity (denoted as CC R- φ D ) can reach a value close to 0.6. Effects of parameters including optical frequency detuning, and modulation depth and noise bandwidth and transparency carrier density for CARP light generation are investigated in detail. By optimizing the optical frequency, modulation depth, and noise bandwidth, respectively, CC R-φD can be reduced to 0.32, 0.18, and 0.10. In the meantime, CC R-φD can be further reduced through secondary optimizing of parameters. CC R-φD can be further reduced by increasing transparent carrier density provided response laser synchronization is achieved. This work gives a new insight about the laser synchronization induced by common CARP light, and also contributes a suggestion of security improvement for physical key distribution based on laser synchronization.

Temperature–strain cross-sensitivity and bending-induced optical loss are two major limitations that challenge the in-situ application of distributed optical fiber sensors. Researchers have attempted to solve these two issues but seldom can overcome both. This paper proposes a novel bending-loss-resistant distributed temperature and strain discriminative sensor that is based on a 98 mol% germania-doped few-mode fiber and a standard Brillouin optical time-domain analysis setup. In a proof-of-concept demonstration, distributed temperature and strain discriminative measurements were conducted under a bending radius of 0.6 cm, where the maximum temperature and strain deviation were 2.78 °C and 33.2 ${\rm{\mu }}\varepsilon$ , respectively.

Optical chaos communication encounters difficulty in high-speed transmission due to the challenge of realizing wideband chaos synchronization. Here, we experimentally demonstrate a wideband chaos synchronization using discrete-mode semiconductor lasers (DMLs) in a master-slave open-loop configuration. The DML can generate wideband chaos with a 10-dB bandwidth of 30 GHz under simple external mirror feedback. By injecting the wideband chaos into a slave DML, an injection-locking chaos synchronization with synchronization coefficient of 0.888 is realized. A parameter range with frequency detuning of -18.75 GHz to approximately 1.25 GHz under strong injection is identified for yielding the wideband synchronization. In addition, we find it more susceptible to achieve the wideband synchronization using the slave DML with lower bias current and smaller relaxation oscillation frequency.